VDDUSB connection

Lukasz Przenioslo · ‎2017-08-22

Posted on August 22, 2017 at 15:07

Hello there,

I have a question regarding VDDUSB connection in STM32L452 MCU. Should it be applied all the time, or only when the USB cable is being connected? I was wondering either it is possible to apply it from the USB cable (with 5 V to 3.3 V conversion) because the device normally runs on battery and I dont want to power the USB module for the time of no USB connection if that is possible. If such solution would be considered, should one reinitialize the USB module in software each time USB is connected? In F4 device there was a dedicated pin for notifying the device that USB was connected. In STM32L4 there are only D+/D- lines available.

I would appreciate all help regarding this issue.

#vdd #stm32l4 #usb

Lukasz Przenioslo · ‎2017-08-23

Posted on August 23, 2017 at 16:53

Yes, I edited my answer. Now I understand this part, thank you.

waclawek.jan · ‎2017-08-23

Posted on August 23, 2017 at 17:06

Yes it's a different EXTI, sorry.

If the PCB is not space-constrained, I'd add two resistors - one from VDDUSB to USB's VBUS, the other from VDDUSB to VDD; and populate only one of them with a 0R depending on circumstances. This allows to measure current during development too.

JW